Well apparatuses have been devised and used wherein precharged accumulators containing pressured fluid are used as operating means for manipulative operation of the tools. Since downhole well pressures, temperatures, and solubilities cannot be accurately calculated or predicted, the precharged accumulators do not always operate adequately because the pressured fluid therein may not be charged at the proper pressure. Downhole well pressure includes the pressure resulting from a standing column of fluid in the well, called the fluid hydrostatic pressure, plus additional pressure, if any, imposed on the fluid column. Since the exact vertical height of the hydrostatic fluid column is not accurately known, and because of the fluid gravity multiplier which must be applied to calculate the hydrostatic pressure or head, the fluid hydrostatic pressure is at least to some degree indefinite. Therefore, if a downhole pressured fluid accumulator needs to be pressured relatively closely equal to or above or below another pressure, such as the casing pressure, it can easily happen that the accumulator fluid pressure precharged at the surface will not be of the proper magnitude when the apparatus containing the accumulator is placed downhole. Further, the magnitude of such precharge pressure may exceed safe pressure ratings for the apparatus case. The present invention seeks to provide apparatus wherein the accumulator pressure is created or modified after the apparatus including the accumulator is in its position of use downhole in the well.